How to Flush Your Vehicle’s Cooling System

If your vehicle’s owner’s manual has instructions for draining the liquid from the cooling system, follow them. If you don’t have a manual, or if it lacks such instructions for flushing the cooling system, follow these steps to flush and change the coolant without endangering the environment.

If you use instructions specific to your car, air is less likely to be trapped in the system after you finish flushing your cooling system.

Park the vehicle in a safe place, away from children and small animals.

Make sure that the engine is cold, the ignition is off, and the parking brake is on.

Place a bucket under the drain valve at the bottom of the radiator.

The bucket should be able to hold at least two gallons of liquid.

Open the drain valve and allow the liquid to drain into the bucket.

Don’t allow the liquid to drain onto the ground or into a storm drain or sewer.

Close the drain valve and pour the used liquid into containers with tight-fitting lids.

Label them clearly as “antifreeze” or “coolant,” and place them away from kids and pets until you can dispose of them safely.

A funnel and some old gallon water jugs do the job as long as you label them prominently and pour carefully to avoid spilling the liquid on the ground.

Open the radiator pressure cap and fill the radiator with water.

Run the engine with the heater control on High for about ten minutes.

Keep an eye on the temperature gauge to make sure that the engine doesn’t overheat. If your vehicle has an engine temperature warning light instead of a gauge, shut off the engine as soon as it lights up.

Shut off the engine and allow it to cool down.

When the radiator is cool enough to touch, drain the water out of the system into the bucket again, and transfer it from there into a closed container for disposal. Label the containers toxic water to prevent accidents.

Close the drain plug and refill the system with water and coolant.

Consult your owner’s manual, the back of the coolant jug, or the charts that coolant manufacturers supply to find out the number of quarts that your cooling system holds. Many coolants are now pre-diluted with water, but if you’re buying straight coolant, divide that number by two and buy that amount of coolant. Adding an equal amount of water to straight coolant gives you a 50/50 water/coolant mixture, which is fine for everything but extremely cold weather.

The liquid should reach the “MAX” line on the coolant recovery reservoir or cover the fins in the radiator. If it doesn’t, continue to add equal parts water and coolant until it does.

Disperse the water and coolant evenly throughout the system.

Replace the pressure cap and run the engine with the heater on High until the temperature gauge reads in the normal range.

Shut off the engine and clean.

Place contaminated rags in sealable plastic bags and put them into the garbage, and store the unused coolant safely away from kids and pets.

After you’ve driven your car for a few days, check the liquid level in the recovery system reservoir again, adding equal parts water and coolant to the reservoir if the level is low.

If it’s low again in a few more days, have the system checked at a service facility.

You can buy products for cleaning the cooling system during the flushing process. These products remove rust and sediment that flushing with plain water can’t. If your cooling system has been cleaned regularly and you want to clean it yourself, buy a well-known brand and follow the instructions on the package carefully.

If your vehicle’s cooling system hasn’t been cleaned for a few years, using a cleaner on the system can free so much sediment that it clogs your radiator or thermostat. Have the system flushed, cleaned, and refilled professionally.